U.S. patent application number 11/197199 was filed with the patent office on 2005-12-01 for generator rotor.
This patent application is currently assigned to Siemens Westinghouse Power Corporation. Invention is credited to Gardner, William Cannon, Light, Kevin, Whitener, Randy Edward, Zhang, Jiping.
Application Number | 20050264124 11/197199 |
Document ID | / |
Family ID | 31977896 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050264124 |
Kind Code |
A1 |
Zhang, Jiping ; et
al. |
December 1, 2005 |
Generator rotor
Abstract
An improved generator rotor (30) and a method of repairing an
existing generator rotor (12) are disclosed. Methods consistent
with the present invention provide techniques for repairing
existing stress-damaged rotors (12) to remove stress-induced cracks
(29), without requiring new retaining rings (16), to significantly
extend the useful life of a generator without the cost and
complexity of conventional repair techniques. Improved generator
rotors (30) consistent with the present invention provide a
tooth-top design that is more resistant to stress-induced cracking
than conventional designs, resulting in new generators with longer
useful lives.
Inventors: |
Zhang, Jiping; (Winter
Springs, FL) ; Light, Kevin; (Maitland, FL) ;
Gardner, William Cannon; (Rock Hill, SC) ; Whitener,
Randy Edward; (Dusseldorf, DE) |
Correspondence
Address: |
SIEMENS CORPORATION
INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Assignee: |
Siemens Westinghouse Power
Corporation
|
Family ID: |
31977896 |
Appl. No.: |
11/197199 |
Filed: |
August 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11197199 |
Aug 4, 2005 |
|
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10259132 |
Sep 27, 2002 |
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6941639 |
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Current U.S.
Class: |
310/214 ;
29/598 |
Current CPC
Class: |
Y10T 29/49009 20150115;
Y10T 29/49725 20150115; Y10T 29/49011 20150115; Y10T 29/49012
20150115; Y10T 29/4973 20150115; Y10T 29/49728 20150115; Y10T
29/49726 20150115; H02K 15/0006 20130101 |
Class at
Publication: |
310/214 ;
029/598 |
International
Class: |
H02K 003/48; H02K
015/10 |
Claims
1-5. (canceled)
6. A generator rotor, comprising: a rotor tooth having a tooth root
and a tooth top, said tooth top including an outboard and an
inboard region for supporting a retaining ring, wherein said
outboard and inboard regions each comprise a retaining-ring land, a
wedge land, and a fillet, wherein said outboard retaining-ring land
has smaller surface area than said inboard retaining-ring land,
with substantially radial sidewalls that transitions to a fillet
having a radius of about 0.5", and wherein said fillet of said
inboard region has a compound radius with an upper radius of about
0.125" and a lower radius of about 0.063".
7. The rotor claim 6 further comprising an outboard and inboard
retaining-ring having a tapered surface with an increasing the
shrink fit interference value in the inboard direction.
8. The rotor of claim 7 wherein said outboard retaining ring seat
has a first taper having a first slope and said inboard retaining
ring seat has a second taper having a second slope.
9. The rotor of claim 6 further comprising a wedge adaptable for
use with said rotor having a wedge relief of about 0.010" to 0.030"
at the contact surface to the rotor tooth.
10. The rotor of claim 9 wherein wedge relief extends from an
outboard end of said rotor to about 0.5" past a shrink fit area of
said wedge.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to electrical
generators, and more particularly to an improved generator rotor
and a method of repairing existing generator rotors to eliminate
stress-induced cracks.
BACKGROUND
[0002] After prolonged use, stress-induced cracks may develop in
the tooth tops of an electrical generators rotor at locations near
the ends of the rotor referred to as rotor-end sections. A
conventional approach to repairing such cracks is disclosed in U.S.
Pat. No. 5,174,011 to Weigelt, which is incorporated by reference
herein in its entirety. Weigelt discloses machining damaged teeth
to remove large sections of stress-damaged material. The nature and
extent of the machining disclosed in Weigelt makes it necessary to
replace the generator's retaining rings. Replacing a generator's
retaining rings adds significant cost and complexity to the repair
of a generator.
[0003] A new approach to refurbishing generators is needed that
facilitates the removal of stress-induced cracks in a generator's
rotor teeth, without requiring the replacement of the generator's
original retaining rings. A new design for newly-manufactured
rotor-teeth is also needed for providing generators that are
resistant to tooth-top stress-induced cracks and to extend the
useful life of generators.
SUMMARY OF THE INVENTION
[0004] With the foregoing in mind, an improved generator rotor and
a method of repairing existing generator rotors are provided.
Improved generator rotors consistent with the present invention
provide a tooth-top design that is more resistant to stress-induced
cracking than conventional designs. Methods consistent with the
present invention also provide techniques for repairing existing
stress-damaged rotors to remove stress-induced cracks, without
requiring new retaining rings.
[0005] These and other objects, features, and advantages in
accordance with the present invention are provided by both methods
and systems. A method is disclosed for repairing a generator rotor
having a rotor tooth with a tooth root and a tooth top, said tooth
top including an outboard and an inboard region for supporting a
retaining ring, wherein said outboard and inboard regions each
comprise a retaining-ring land, a wedge land, and a fillet. The
method comprising the steps of (a) inspecting said fillet of said
outboard region with a non-destructive testing means to determine
the maximum depth cracks in said fillet; (b) when said maximum
depth of said cracks in said outboard fillet are less than or equal
to about 0.03", removing at least about 0.06" of material beyond
said fillet and directly radial, whereby said wedge land of said
outboard region is removed; (c) when said maximum depth of said
cracks in said outboard fillet are greater than about 0.03" and
less than about 0.07", removing about 0.03" of material beyond said
maximum depth of said cracks and directly radial, whereby said
wedge land of said outboard region is removed; (d) inspecting said
fillet of said inboard region with a non-destructive testing means
to determine the maximum depth cracks in said fillet; (e) when said
maximum depth of said cracks in said inboard fillet are less than
or equal to about 0.03", removing at least about 0.03" of material
beyond said fillet; and (f) when said maximum depth of said cracks
in said inboard fillet are greater than about 0.03" and less than
about 0.06", removing about 0.03" of material beyond said maximum
depth of said cracks.
[0006] A generator rotor is also disclosed that comprises a rotor
tooth having a tooth root and a tooth top, said tooth top including
an outboard and an inboard region for supporting a retaining ring,
wherein said outboard and inboard regions each comprise a
retaining-ring land, a wedge land, and a fillet, wherein said
outboard retaining-ring land has smaller surface area than said
inboard retaining-ring land, with substantially radial sidewalls
that transitions to a fillet having a radius of about 0.5", and
wherein said fillet of said inboard region has a compound radius
with an upper radius of about 0.125" and a lower radius of about
0.063".
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates a conventional rotor assembly.
[0008] FIG. 2 illustrates a perspective view of the rotor assembly
of FIG. 1, with the retaining ring removed.
[0009] FIG. 3 is a flowchart illustrating a method consistent with
the present invention.
[0010] FIG. 4 illustrates the formation of an outboard region of a
rotor-tooth top consistent with the present invention.
[0011] FIG. 5 illustrates the formation of an inboard region of a
rotor-tooth top consistent with the present invention.
[0012] FIG. 6 illustrates a wedge consistent with the present
invention.
[0013] FIG. 7 illustrates a new or repaired rotor consistent with
the present invention.
DETAILED DESCRIPTION
[0014] Electrical generators utilized in the power-generation
industry typically include a rotor with two retaining-ring
assemblies like the one illustrated in FIG. 1. The rotor assembly
10 includes a rotor 12, aligned for rotation about a longitudinal
axis 14 and a retaining ring 16, installed on each end of the rotor
12. The rotor 12 includes a tooth region 18 with multiple
longitudinal slots 20 defining a plurality of longitudinal teeth
22. Field windings 24 are disposed between the longitudinal teeth
22 and within the slots 20. The field windings 24 run the length of
the rotor and make turns at each end of the rotor 12 to form end
turns 28.
[0015] When the rotor assembly 10 is spinning, a radially-outward
centrifugal force is exerted on the windings 24 and the end turns
28. In order to retain the field windings 24 tightly within the
slots 20, wedges 26 are positioned in the openings of the slots 20.
However, the end turns 28 extend beyond the rotor slots 20 and are
not retained by these wedges. In order to restrain the end turns
28, a retaining ring 16 is installed over each end of the rotor 12.
The inside diameter of retaining ring 16 is formed with an inside
diameter that is slightly smaller than the outside diameter of the
rotor 12. During the manufacturing of the rotor assembly 10, the
retaining ring 16 is heated to expand is inside diameter to
facilitate its installation over the rotor 12. When the retaining
ring 16 cools, a shrink fit is created between the retaining ring
16 and the rotor 12.
[0016] FIG. 2 illustrates an enlarged perspective view of the tooth
region 18 of FIG. 1. The retaining ring 16 has been omitted for
clarification. As illustrated in FIG. 2, windings 24 are restrained
by wedges 26 within a longitudinal slot 20 formed between adjacent
teeth 22. When the rotor assembly is spinning, the windings 24 and
wedge 26 exert a radially-outward force on the tooth tops 23 at the
wedge lands 25. The shrink-fitted retaining ring exerts an opposing
radially-inward force on the wedge 26 and the retaining-ring lands
28. When the rotor assembly is not spinning (for example, during
idle periods), the radially-inward force exerted by the
shrink-fitted retaining ring is not balanced by the centrifugal
forces exerted on the wedge 26. As a result, the tooth tops 23 tend
to be subjected to excessive stresses when a generator is cycled on
and off. These stresses tend to form cracks 29 near the filets 27
of the tooth tops 23. The more frequently a generator is cycled,
the more likely such cracks are to form.
[0017] FIG. 3 illustrates a method of repairing a generator rotor
consistent with the present invention. When an electrical generator
is disassembled for repair, the outboard sections of the rotor are
inspected using a non-destructive test, such as an ultrasonic or
eddy-current test, to determine the depth of the stress cracks in
the area near the fillets of the tooth top (step 100). If the
cracks detected have a maximum depth of less than or equal to about
0.03" (decision 105), then at least about 0.06" of the
outboard-retaining-ring land 28 is removed beyond the fillet and
directly radial by a horizontal mill or other suitable machining
device 400, as illustrated in FIG. 4 (step 110). If the cracks
detected have a maximum depth of greater than about 0.03" and less
than about 0.07" (decision 115), then about 0.03" of the
outboard-retaining-ring land 28 is removed beyond the largest crack
depth and directly radial, as illustrated in FIG. 4 (step 120). If
the cracks detected have a maximum depth of greater than about
0.07", the method of the present invention may not be suitable for
repairing the rotor.
[0018] The inboard-retaining-ring land is also inspected using a
non-destructive test to determine the depth of the stress cracks in
the inboard fillets (step 125). If the cracks detected have a
maximum depth of less than or equal to about 0.03" (decision 130),
then at least about 0.03" of rotor material is removed beyond the
fillet by a horizontal mill or other suitable machining device 500,
as illustrated in FIG. 5 (step 135). The fillet may be machined,
for example, in an inboard direction for the length of the
retaining ring land or beyond the retaining ring land for a short
distance. If the cracks detected have a maximum depth of greater
than about 0.03" and less than about 0.06" (decision 140), then
about 0.03" of rotor material is removed beyond the largest crack
depth (step 145). If the cracks detected have a maximum depth of
greater than about 0.06", the method of the present invention may
not be suitable for repairing the rotor.
[0019] In one embodiment of the present invention, the retaining
ring lands of the outboard and inboard regions are also machined to
form a tapered shrink fit with a height (or radius) that decreases
in an inboard direction. The tapered shrink fit interference values
vary depending on the rotor diameter, the retaining ring thickness,
and the length of the shrink fit. The tapered shrink fit ensures a
more uniform stress distribution and minimizes the alternating
cyclic fatigue stresses.
[0020] In another embodiment of the present invention, a wedge 600
(illustrated in FIG. 6) for use with the rotor may be machined to
form wedge reliefs 610. The wedge reliefs provide the allow the end
wedges to have additional radial movement so that the centrifugal
load can be transferred fully or partially to the retaining ring at
speed. In this way, the rotor tooth top is subjected no load or
partial load from the winding in the slot at speed. Typical wedge
relief values used are around 0.010" to 0.030". For rotors with 930
mm outer diameter, a wedge relief of 0.020" has been applied over
the length of 3.57" from the end. For a rotor with 1075 mm outer
diameter, a wedge relief of 0.020" has been applied over the length
of 3.75" from the end.
[0021] The features of the improved rotor-tooth top described above
may also be incorporated into newly-manufactured rotors to form an
improved rotor with an increased resistance to stress-induced
cracking. FIG. 7 illustrates a new rotor with an improved
rotor-tooth top 30 consistent with the present invention. The
improved rotor-tooth top 30 includes an outboard-end section 32 and
an inboard-end section 34. The outboard-end section 32 has an
enlarged fillet 36 and a substantially radial side-wall 38. The
inboard-end section 34 also has an enlarged fillet 40. The
dimensions of the enlarged fillet 36 and side-wall 38 in new rotors
will vary depending on the dimensions of the rotors. The dimensions
of the enlarged fillet 36 and the side-wall 38 in repaired rotors
will vary depending upon the dimensions of the rotors and the depth
of the stress cracks found during inspection.
[0022] The present invention has been described with reference to
the accompanying drawings that illustrate preferred embodiments of
the invention. The invention may, however, be embodied in many
different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art. Thus, the scope of the invention should be determined
based upon the appended claims and their legal equivalents, rather
than the specific embodiments described above.
* * * * *